1. Field of the Invention
The invention relates to a system for magnetically shielding a charged particle lithography apparatus.
2. Description of the Related Art
In the semiconductor industry, an ever increasing desire exists to manufacture smaller structures with high accuracy and reliability. Charged particle lithography is a promising technology to meet the high demands. In this type of lithography charged particles are manipulated to transfer a onto a target surface of a substrate, typically a wafer. Because the manipulation of charged particles is performed using controlled electromagnetic manipulation, the accuracy of charged particle lithography may decrease if the lithography system is exposed to external electromagnetic fields.
For this reason a various magnetic shielding techniques have been developed for protecting charged particle lithography systems from external magnetic fields. For example, the charged particle lithography system may be enclosed in one or more layers of a material that has a high magnetic permeability. However, such shielding may be insufficient to sufficiently reduce the external fields. Furthermore, the shielding is incapable to compensate for fluctuating magnetic fields.
Another example to protect charged particle systems from external magnetic fields is the use of one or more pairs of coils capable of generating fields in a predetermined direction such that external magnetic fields can be cancelled out by the fields generated by the coils. The use of one or more coil pairs may operate perfectly well for controlling the magnetic field to which a single charged particle system is exposed. However, in the semiconductor industry of the future it is foreseeable that multiple charged particle lithography systems will operate in proximity of each other. As a result, generating a compensation field may solve the negative influence of an external field for one charged particle lithography system, while the generated compensation field acts as a disturbing external field for an adjacent charged particle system.